This invention relates to processing aids for further processing in synthetic polymers, comprising finely divided inorganic solids, selected from pigments and/or fillers.
Processing aids are substances or mixtures which can be incorporated in synthetic polymers as functional additives; as fillers and/or pigments they should ensure improved or additional technical properties as compared to the unfilled product and/or have pigment-specific properties, i.e. there is no clear-cut dividing line between filler and pigment.
To ensure that fillers and pigments, which are present in the form of a powder, can be incorporated in synthetic polymers as functional additives and can fully show their effect, the same require a pretreatment which involves a considerable effort.
This pretreatment usually includes the following process steps:
introducing the pigment and/or filler in a liquid medium
predispersing by using weak shearing forces, e.g. by means of dissolver or rotor-stator systems
fine dispersing by using strong shearing forces, e.g. by means of stirrer mills
further processing steps, such as centrifuging, depositing and/or filtering.
In particular the energy-rich and thus cost-intensive process step of fine dispersing is used for grinding and homogeneously distributing the starting products which are generally present in the form of agglomerates. The pigment or filler suspension prepared by the user with such an effort can be supplied to the actual polymer production process.
A further possibility is to directly add the solids as powder or in the form of master batches to the process of producing the synthetic polymers.
In both cases, the solids must be distributed in the molten highly viscous polymer; there are considerable dosage problems, as the solids to be designated as blunt substantially aggravate a uniform introduction thereof. Moreover, in the extrusion step there is provided a polymer melt with a viscosity of up to 500 Pa.s, in which there are no high enough shearing forces in order to comminute solid agglomerates.
It is the object of the present invention to provide processing aids as described above for further processing in synthetic polymers, which can homogeneously be dispersed in the same easily and with little effort.
This object is solved in that the finely dispersed solids are embedded in a carrier material, selected from at least one of the organic substances polyols, polyglycols, polyethers, dicarboxylic acids and the derivatives thereof, adipic hexamethylenediamine, caprolactam, paraffins, phosphoric acid ester, hydroxycarboxylic acid ester and cellulose.
As material for the solids there may in particular be used titanium dioxide, barium sulfate, calcium carbonate, lithopones, silica, alumosilicates, zinc sulfide, alumina, kaolins, talcum, dolomites and calcites.
In accordance with the preferred aspect of the invention, the content of solids in the processing aids is 0.2 to 35 wt-%, in particular 10 to 30 wt-%.
Since the particle size of the inorganic solids is 0.01 to 10 xcexcm, preferably 0.1 to 0.8 xcexcm, good properties can be achieved therewith as regards delustring, in particular of synthetic fibers.
To avoid oxidation phenomena in the organic substance, the same still contains up to 5 wt-%, preferably up to 2 wt-%, of at least one of the commercially available antioxidants such as Irganox 1010, Cibatex 4458, Irganox 1098, and Irganox B 1171 (manufacturer: Ciba Spezialitxc3xa4ten Chemie GmbH, Lam-pertheim).
In accordance with the further embodiment of the invention, the organic substance consists of polyethylene glycol with molar weights of 1000 to 3000. This substance has a good wettability and a good embedding capacity for the inorganic solids.
The processing aid present with a particle size of 3 to 100 xcexcm is free-flowing, easy to meter and easy to disperse. In addition, the solids contained in the processing aid are free from oversize particles and exhibit no tendency towards reflocculation. The processing aid can be dispersed in synthetic polymers with relatively low shearing forces.
The production of the processing aids is effected such that an aqueous master batch containing 20 to 60 wt-% solids is dispersed with 0.2 to 50 wt-% (based on the solids content) organic substances, the dispersion is ground wet to a mean particle size d50 of 0.1 to 0.8 xcexcm, the content of particle sizes  greater than 1 xcexcm is separated, and then the dispersion is dried.
In accordance with the further aspect of the process measures wet grinding is effected in a stirrer ball mill, the separation of oversize particles  greater than 1 xcexcm is effected by depositing, filtering or centrifuging, and drying the suspension is effected by spray drying or mill drying.